1. Field of the Invention
The present invention generally relates to a lighting device for vehicles, and more particularly to a lighting device for head lamp apparatus which transmits rays of light from a central light source to head lamps through optical fibers.
2. Description of the Related Art
As a conventional type of such lighting device, for example, disclosed in the U.S. Pat. No. 4,958,263 (corresponding to the Japanese Unexamined Patent Publication No. 2-172102), a method of transmitting the rays of light from a central light source to the head lamps through optical fibers has recently been examined.
As a related work (not known) for such lighting device, the applicant of the present invention has proposed a lighting device for vehicles as shown in FIG. 6, and filed an U.S. patent application Ser. No. 08/78088 (corresponding to the Japanese Patent Application No. 4-344404 which was published Mar. 11, 1994 under No. 6-68702). In FIG. 8, the lighting unit 50 transmits rays of light from a central light source (not shown) to a flat light lens 52 and a hot zone lens 53 through an optical fiber 51. The transmitted rays of light are then permeated through the flat light lens 52 and the hot zone lens 53 so as to be irradiated as illuminating rays of light. As a connecting surface W between the flat light lens 52 and the hot zone lens 53 is generally expected to be a total-reflection surface, all rays of light having been incident into the flat light lens 52 propagates the inside of the flat light lens 52, and on the other hand, all rays of light having been incident into the hot zone lens 53 propagate the inside of the hot zone lens 53.
According to the above configuration, however, connecting surfaces of the flat light lens 52 and the hot zone lens 53 are contacted along the connecting surface W, and part of the rays of light which should permeate the inside of the flat light lens 52 may enter into the hot zone lens 53 and be irradiated forwards from light emitting surface 55 along a light track 56 shown with two-dot chain line in FIG. 8.
On the other hand, the rays of light having been incident into the flat light lens 52 and the hot zone lens 53 are irradiated forwards from light emitting surfaces 54 and 55 directly or after being reflected by the connecting surface a respectively. As shown in FIG. 8, the rays of light scattered at a corner portion d of the lens incidence surface are partly reflected by a surface X along a light track 57 with a large incident angle, and also partly reflected by a surface Y along a light track 58.
Light distribution curve of the illuminating rays of light irradiated by the above lighting unit 50 for vehicles is shown in FIG. 9. FIG. 9 shows the light distribution pattern which is irradiated on a screen disposed in a predetermined distance forward of the vehicle. That is, there is a problem with this device that the light tracks 56, 57 and 58 are located above a cut line C and dazzling rays of light are caused to irradiate to oncoming vehicles. In FIG. 9, a light distribution curve 59 shown with a solid line is generated by the rays of light emitted from a light emitting surface 55 of the hot zone lens 53, and a light distribution curve 60 shown with a broken line is generated by the rays of light emitted from a emitting surface 54 of the flat light lens 52. Shades 61 and 62 shown in FIG. 10 are disposed between the optical fiber 51 and the flat light lens 52 and hot zone lens 53, and depending on the shape of the shades 61 and 62, the light distribution curves 59 and 60 shown in FIG. 9 are contoured.